As far as I can tell, when the Main and Aux cameras are scaled to 100%, they are 1.1 Poser Native Units (PNU), (or approximately 2883.4 mm) in front of (in the positive z direction) the position indicated on their DollyZ dial. My value of 1.1 PNU may not be exact, but should be accurate to within 0.05 PNU. The center of their orbit is this point 1.1 PNU in front of the position indicated on the DollyZ dial.

As far as I know Dolly cameras are at exactly the position shown on the dials.